Simultaneous effect of strain rate and humidity on the structure and mechanical behavior of spider silk

Spider dragline silk fibers are important in nature for capturing prey and as a lifeline. However, spider silk is exposed to a range of humidity and deformation conditions, and it is important to understand what effect these have on its properties. Here, we simultaneously investigated the effect of a wide range of strain rates on the structural and mechanical properties of spider silk under different humidity conditions. The toughness of the silk fiber was enhanced under mild humidity and high deformation rate conditions, which occur in the natural habitat of spiders. Structural changes in the fiber upon tension were monitored with a wide-angle X-ray scattering system, showing that during stretching the orientation of the crystalline β-sheets aligned, whereas the crystallite size decreased. These findings help to understand the link between the structural changes and mechanical behavior of spider silk. Spider silk is well known for its high toughness. Here, a comprehensive study of the simultaneous effect of strain rate and humidity on toughness is reported, revealing that toughness is highest under mildly humid conditions and at high strain rates, similar conditions to those in nature.